MEMS is an aberration of microelectromechanical system. That is, MEMS indicates technology of manufacturing electromechanical systems on one chip by manufacturing and mounting micro mechanical components, sensors, actuators, and electronic components on a semiconductor wafer substrate by using semiconductor process and micromachining technologies. Such three-dimensional MEMS microstructure is essentially included in various micro systems such as accelerator sensors and micro switches. To mechanically drive or sense by using the three-dimensional MEMS microstructure, it is required to manufacture the microstructure floated leaving a certain space from a substrate to freely move.
As described above, to float the microstructure with the certain space from the substrate, a sacrificial layer is formed between the substrate and the microstructure in manufacturing the three-dimensional MEMS in such a way that the microstructure is separated from the substrate with a predetermined space. The sacrificial layer is selectively removed, thereby floating the microstructure from the substrate.
Generally, as a method of removing a sacrificial layer, there is used wet etching of removing the sacrificial layer by putting a microstructure and a substrate with the sacrificial layer formed therebetween, in an etching solution. When the sacrificial layer is removed by the wet etching, a residual etching solution is cleaned and removed by using a cleaning solution such as deionized water, methanol, and isopropyl alcohol.
However, in the case, while the cleaning solution used to remove the etching solution is vaporized, capillary force occurs due to surface tension of the cleaning solution present between the substrate and the microstructure. Generally, since the capillary force is greater than restitution force of the microstructure, the microstructure sticks to the substrate. The microstructure sticking to the substrate is not separated from the substrate due to electrostatic force and van der Waals forces after the cleaning solution is perfectly vaporized, which is designated as stiction.
As described above, as a method of preventing stiction occurring while removing a cleaning solution, there is supercritical CO2 drying method of replacing a cleaning solution by a carbon dioxide liquid, controlling a temperature and pressure to a supercritical point, and using phase transfer characteristics to a supercritical fluid.
As another method, there is a method of removing a sacrificial layer by using a gaseous etching material. According to this method, instead of wet etching using an existing hydrogen fluoride to remove an oxide sacrificial layer, the oxide sacrificial layer is removed using an anhydrous hydrogen fluoride.
The supercritical CO2 drying method has problems in which a process is complicated, a complicated apparatus is required to form, maintain and control a supercritical state, it is very difficult to manage specimen according to a size thereof, and it is not suitable for mass production.
Also, the method of removing the oxide sacrificial layer in a gaseous state has problems in which a process is complicated, there is a possibility of generating stiction since water is formed while the hydrogen fluoride reacts as an oxide, and it is limited to the case of an oxide sacrificial layer.